Policy and charging control comprises functions used in telecommunication systems to enable providers of telecommunication services to provide quality of service (QoS) functions and/or charging control, particularly in packet-switched respectively connectionless communication systems, for example IP-based service data flows. Policy decisions, e.g. decisions regarding acceptance of a particular service request and/or the provision of a certain bandwidth or bitrate for a service request, may be based on subscription information of a user requesting said service, bandwidth request of the requested service, and other information related to the network and services.
Such a policy control system is e.g. known from the Policy and Charging Control (PCC) architecture defined for the 3GPP evolved packet system (EPS) as documented in 3GPP Tech. Spec. 23.203, “Policy and Charging Control Architecture”, Release 9, 2009.
The reference network architecture for PCC defined in the mentioned 3GPP specification is shown in FIG. 1. The PCC functionality is comprised by the functions of the Policy and Charging Enforcement Function (PCEF) 1, the Bearer Binding and Event Reporting Function (BBERF) 2, the Policy and Charging Rules Function (PCRF) 3, the Application Function (AF) 4, the Online Charging System (OCS) 5, the Offline Charging System (OFCS) 6 and the Subscription Profile Repository (SPR) 7.
The PCRF 3 is the policy engine of PCC which combines the service data flow description received over the Rx reference point and the input received from the Gx and Gxx reference points with user-specific policies and data from the subscription profile repository (SPR) 7 to form session level policy decisions and provides those to the PCEF 1 and the BBERF 2. The PCEF 1 enforces policy decisions received from the PCRF 3 and also provides the PCRF 3 with user- and access-specific information over the Gx reference point. The charging related information received over the Gx interface is further used when it interacts with the OCS 5 and OFCS 6. The PCEF 1 is usually located in a Gateway (GW; e.g., the PDN-GW in EPS).
When a mobile IP protocol is used between an access Gateway (e.g., the S-GW) and the PDN GW, the PDN GW has no knowledge of the bearers. The BBERF 2 was introduced into the architecture to handle this situation. The PCRF 3 provides the authorized QoS to the BBERF 2 over the Gxx reference point. The BBERF 2 detects events and reports them over the Gxx interface. The BBERF 2 is also responsible for service data flow detection, resource reservation and QoS control. The location of BBERF 2 depends on the particular access network. For example, for the 3GPP networks, the BBERF 2 (if applicable) is located in the serving gateway (SGW), whereas for HRPD (High Rate Packet Data) access network, the BBERF 2 is located in the HSGW.
In the described PCC architecture and also in some other policy control architectures, the policy decision function and policy enforcement function are distributed and put into different network elements. For example, in PCC the PCRF 3 is in charge of the policy provisioning and decision, while the PCEF 1/BBERF 2 is responsible for the installation and enforcement of the policy decision from the PCRF 3. The PCRF 3 usually makes the policy decision based on the inputs received from AF 4, SPR 7 and possibly other network entities.
In PCC a policy (including GBR, guaranteed bitrate services) request is always granted by the PCRF if requirements given by subscriber status etc. are met.
In cases where there is not enough bandwidth resource for a request, the PCEF shall drop some existing service flows or bearers with lower Allocation Retention Priority (ARP) value than the incoming request. In an even worse case, when there are no low priority flows or bearers having Pre-emption-Vulnerability enabled anymore in the PCEF 1, even newly incoming important policy requests can not be admitted.
A particular drawback of the existing solution is that, when the PCEF or BBERF is in overload with regard to control plane (i.e., the signaling load is heavy), the signaling exchange with the PCRF could deteriorate the situation further. In PCC, the PCEF or BBERF shall inform the PCRF about the result of a PCC rule operation received from the PCRF. If the PCEF can not finish the PCC rule enforcement successfully, the PCRF may resend the policy decision to the PCEF with or without modification. The signaling exchange, partly caused by the overload situation itself, will make the overload worse, potentially even resulting in a breakdown of parts of the network.
Such overload or congestion situations may particularly occur during emergency situations, e.g. major accidents, natural disasters like floods, earthquakes, hurricanes etc., terrorist attacks, and virtually any conceivable situation in which national security and/or public safety are affected. In such cases, network load will be high, and it may even be that the communication infrastructure itself is affected, but it will be of vital interest that at least important communication requests will be served, like the ones of emergency forces or administrative or governmental units.
But even under usual circumstances, a gateway in the core network, e.g. the gateway on which the PCEF resides, may get into a congestion or overload status due to an unexpected traffic burst or with the rapid data traffic increase in a future EPS network in which the RAN (Radio Access Network) gets high speed transfer rate. In such a situation, in which a gateway is in a status of high load, many existing bearers or Service Data Flows (SDFs) will be dropped to admit potential higher priority policy requests. In some cases, some low priority PCC rules may be admitted when PCEF has the required resource temporally, but soon later may be pre-exempted by higher priority rules when the load on the PCEF increases again. In such a case, low priority requests will be admitted and dropped soon. This may degrade the end-user's experience and satisfaction degree.